// Copyright (c) 2021, gottingen group.
// All rights reserved.
// Created by liyinbin lijippy@163.com


#ifndef ABEL_DIGEST_CRC32C_H_
#define ABEL_DIGEST_CRC32C_H_

#include <stddef.h>
#include <stdint.h>

namespace abel {

namespace crc32c {

extern bool is_fast_crc32_supported();

// Return the crc32c of concat(A, data[0,n-1]) where init_crc is the
// crc32c of some string A.  extend() is often used to maintain the
// crc32c of a stream of data.
extern uint32_t extend(uint32_t init_crc, const char *data, size_t n);

// Return the crc32c of data[0,n-1]
inline uint32_t value(const char *data, size_t n) {
    return extend(0, data, n);
}

static const uint32_t kMaskDelta = 0xa282ead8ul;

// Return a masked representation of crc.
//
// Motivation: it is problematic to compute the CRC of a string that
// contains embedded CRCs.  Therefore we recommend that CRCs stored
// somewhere (e.g., in files) should be masked before being stored.
inline uint32_t mask(uint32_t crc) {
    // Rotate right by 15 bits and add a constant.
    return ((crc >> 15) | (crc << 17)) + kMaskDelta;
}

// Return the crc whose masked representation is masked_crc.
inline uint32_t unmask(uint32_t masked_crc) {
    uint32_t rot = masked_crc - kMaskDelta;
    return ((rot >> 17) | (rot << 15));
}

}  // namespace crc32c
}  // namespace abel

#endif  // ABEL_DIGEST_CRC32C_H_
